Vehicle air conditioning compressors are generally powered by an accessory belt taking power from the engine, with a clutch controlling when the compressor is driven at full capacity by the engine and when it is disconnected. One of the concerns with this conventional arrangement is that the compressors operate at full capacity at all times the clutch is engaged. This is not optimal for some driving conditions, and thus, some air conditioning systems have taken to cycling the compressor clutch on and off. However, this can create stumble in the engine operation, thus degrading the ride for the vehicle occupants. Consequently, others have attempted to vary the capacity of the compressor itself during operation, in one way or another, in order to allow for a more optimal compressor output, without having to cycle the compressor clutch on and off as frequently.
Some vehicle air conditioning systems use rotary compressors which employ vanes for sealing around an eccentric rotary member to compress the refrigerant. This particular type of air conditioning compressor employs an eccentric rotating part rotating in a cavity with vanes sealing against it to form pump cavities (gas chambers) for compressing the refrigerant. Rolling piston compressors operate on the principle that refrigerant gas is trapped and compressed between a rotating rotor and a reciprocating vane. If the vane is restrained from moving, then, the compressor displacement (i.e., capacity) will be reduced. One way to accomplish this is with a solenoid, which when energized causes an armature to contact the vane and prevent its movement from a retracted position. This locks the vane away from the rolling piston so that its edge does not bear on the rolling piston, thus exposing the outlet port to the inlet port and preventing compression. An example of a system such as this is disclosed in U.S. Pat. No. 4,397,618 to Stenzel.
In a rolling piston compressor, generally, the width of a compressor vane is held to very tight tolerances as is the slot within which it slides in order to allow for a snug fit, creating sealing between the two. A concern arises with the use of an armature being employed to stop the motion of the vane during periods of vane deactivation in that the armature may cause deformation in the surface of the vane as the two repeatedly engage and disengage. There is potential, when the armature is actuated, that as it stops the vane movement (causing impact between the back of the hole and the armature), this impact of the armature with the back of the hole in the vane will cause the material at the back of the hole (i.e., on the spring side of the hole) to yield and deform somewhat through normal usage and extend outward like a small burr on the vane surface. Any deformation which causes the surface of the vane to extend outward forming a burr can increase wear between the vane and the slot, due to the tight clearance, and even possibly cause one to jam relative to the other. The result of the rubbing of the burr on the vane wall, then, may be that the maximum capacity of the compressor is reduced.